What JWST found in the extreme outer Milky Way

Bright stars and dust lanes dominate our everyday views of galaxies.

This rotating spiral galaxy, NGC 1512, is located only 30 million light-years away, and is highlighted by a core of old stars, a central ring of hot, star-forming material, and then wispy, thin spiral arms connect it to a more ring-like, star-rich region in the outskirts. This Hubble/JWST composite image showcases the stark differences between what optical telescopes, like Hubble can see, with the network of gas and dust revealed by JWST in infrared light. The overwhelming majority of rich dusty, stellar, and gaseous features are found in the inner portions of galaxies such as this.

Supremely interesting features occur, visually, within a galaxy’s innermost regions.

The European Space Agency’s space-based Gaia mission has mapped out the three-dimensional positions and locations of more than one billion stars in our Milky Way galaxy: the most of all-time. Looking toward the center of the Milky Way, Gaia reveals dusty, gaseous, and stellar features that are scientifically and visually fascinating.

This holds true within our Milky Way, where we observe 27,000 light-years from the center.

Looking away from the galactic center rather than toward it, this unfamiliar view of the MIlky Way comes from the ESA’s Gaia mission. This view spans roughly 120 degrees from left-to-right: roughly double what the human eye can perceive at once.

However, looking away from the galactic center, an unfamiliar view greets us.

Looking toward the region of our galaxy, in the outskirts, where the Digel clouds are located looks, in visible light, like a dark and irregular dust cloud superimposed atop a canopy of stars. In reality, this gas-and-dust-rich region of the Milky Way’s plane is currently forming new stars, even in the galactic outskirts.

The sparse galactic outskirts contain fewer stars and less gas.

This image shows roughly the same region as was highlighted in the Gaia view preceding it, but showcases hydrogen-rich star-forming regions, as well as the two Digel clouds, labeled 1 and 2 as well as with their various sub-complexes. These two clouds were the target regions of the new JWST study.

The material is also less enriched, and less likely to form rocky planets.

This color-coded map shows the heavy element abundances of more than 6 million stars within the Milky Way. Stars in red, orange, and yellow are all rich enough in heavy elements that they should have planets; green and cyan-coded stars should only rarely have planets, and stars coded blue or violet should have absolutely no planets at all around them. Note that the central plane of the galactic disk, extending all the way into the galactic core, has the potential for habitable, rocky planets. but that stars facing away from the galactic center (far left and right) are much lower in heavy element abundance.

Nevertheless, new episodes of star formation occur within the extreme outer galaxy.

This map of the neutral hydrogen density and distribution in and around the two Digel clouds located in the outskirts of our Milky Way highlights several regions of interest, which were imaged by JWST’s NIRCam and MIRI instruments in a variety of wavelength filters.

A new set of JWST observations unveils those star-formation episodes in unprecedented detail.

Located roughly 58,000 light-years from the galactic center, Digel cloud 2s, highlighted here, is found in the extreme outer galaxy of the Milky Way. The main cluster, glittering brilliantly, exhibits at least five independent protostellar jets, as highlighted by the white arrows.

JWST’s near-infrared views are up to 80 times more sensitive than the ground-based Subaru telescope for:

• Digel cloud 1a,

This animation switches between near-infrared views acquired with the ground-based 8.2 meter Subaru telescope and the space-based 6.5 meter JWST’s NIRCam imager. The sensitivity, sharpness, and resolution of JWST, despite its smaller size, is 10-80 times as great as that of Subaru for this object.

• Digel cloud 2n,

Subaru (blurred) and JWST (sharper) views of Digel cloud 2n, in the same wavelengths of light, showcasing JWST’s superior capabilities. Note that many stars that are blurred and/or unresolved in the Subaru imagery are clear, and some are even shown to be multi-star systems, to JWST’s eyes.

• and Digel cloud 2s.

Within the dusty nebular complex of Digel cloud 2s, as revealed coarsely by Subaru but in finer detail by JWST, many protostars, including jet-like features, can be seen. Some objects look very similar to background galaxies within the cluster, but are just as likely to be protostars wrapped in a dusty cocoon.

Spitzer’s longer-wavelength views are even more spectacularly surpassed by JWST’s.

Although JWST is often called the “successor to Hubble,” it is more accurately the successor to Spitzer, which viewed comparable wavelengths of infrared light. Here, the spectacular enhancement in scientific value from Spitzer to JWST is showcased, as the stars, resolution, as well as gassy, dusty, and jet-like features all are revealed by JWST, whereas Spitzer could not resolve them.

Stars of all masses, brown dwarfs, and even protostellar jets shine brilliantly.

This image shows the same high-resolution region of space as imaged with JWST in six different wavelengths of light. By combining different wavelengths of light, protostellar jet features (especially in the lower-right panel) can clearly be seen.

Near-infrared and mid-infrared views, both acquired by JWST, reveal vastly different details.

This image shows a composite of the various JWST NIRCam filters used to image Digel cloud 1a in the Milky Way’s outskirts. Newborn stars shine brilliantly, and are highlighted within the various outlined boxes.

Digel cloud 1a houses a fascinating newborn star cluster.

Complementary to the previous NIRCam image, the JWST composite MIRI image of Digel cloud 1a reveals cooler, longer-wavelength features, including warm dust and shrouded protostars that are invisible to NIRCam’s views.

Wispy, dusty features paint a ghostly silhouette in Digel cloud 2n.

Digel cloud 2n, as imaged by NIRCam in three separate filters here, is much richer in gas and dust than Digel cloud 1a, with large populations of newborn stars highlighted in the outlined boxes.

A still-forming protostar shines in mid-infrared light.

As highlighted in the box labeled “c” in this MIRI image of Digel cloud 2n, a star that’s barely visible at all in the complementary NIRcam image shines a brilliant red. This likely indicates a newly-forming protostar shrouded in a cocoon of neutral matter. The protostar itself may still be growing, or may be beginning to shine under its own power.

Finally, jets and outflows highlight Digel cloud 2s.

The largest star-forming region known, so far, within the extreme galactic outskirts of the Milky Way can be found in the box labeled “a” in this NIRCam image of Digel cloud 2s. This star cluster contains more than 100 member stars, as newly revealed by JWST’s unprecedented resolution.

These newborn clusters, someday, may harbor fully inhabited worlds.

Although the stars shown here by JWST’s MIRI in Digel cloud 2s are far too young to harbor life at present, many of these stars may wind up being inhabited worlds several billion years from now. Whether these stars possess rocky planets or not will require a follow-up set of observations, and possibly a future observatory.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.